1. Field of the Invention
This invention relates to a magneto-optical recording-reproducing system capable of recording, reproducing and/or erasing information on a recording medium by the use of a beam of light and a magnetic field.
2. Related Background Art
A magneto-optical recording-reproducing system capable of rewriting by the use of a magneto-optical disc as a recording medium is utilized in a data file system or the like because of its high recording density, its great recording capacity and the portability of the recording medium.
In a system according to the prior art, in a case of data rewriting, a first scanning in which a bias magnetic field is first applied to a desired portion to be rewritten in a direction opposite to that during recording and light is continuously applied thereto has been effected to thereby erase old data, and then a second scanning in which the direction of the bias magnetic field is made equal to the direction of recording relative to said desired portion in which the old data have been erased and light modulated in conformity with information is applied to said desired portion has been effected to thereby record new data. In such a method, however, a considerable time is required for access and a large amount of electrical power is required for a bias coil.
So, in recent years, two overwriting methods, i.e., a magnetic field modulation overwrite system and a light intensity modulation overwrite system, have been studied and developed [e.g. the Transactions of the Institutes of Electronics, Information and Communication Engineers of Japan, MR87-61, pp. 19-25 (1987)].
The magnetic field modulation system is a method of providing a floating magnetic head on a side opposite to the light incidence side of a magneto-optical recording medium, rapidly reversing the direction of a bias magnetic field by the floating magnetic head while applying a laser beam, thereby overwriting, and the size of a recording bit is determined by the spot diameter of the laser beam and the magnetic field reversing time of the floating magnetic head [e.g. Japanese Laid-Open Patent Application No. 63-217548]. On the other hand, the light intensity modulation system is one such that two recording layers are formed and one of the two layers is used as a bias layer and recording/erasing is effected by the magnitude of the power of a laser beam.
The present invention is related to the former, i.e., the magnetic field modulation system. In the magnetic field modulation system, a floating magnetic head formed of a ferrite material such as Mn-Zn ferrite is operated in synchronism with an optical head unit on the light incidence side and therefore, a floating mechanism is simplified as much as possible and the weight thereof is reduced. The magnetic head is in contact with the surface of a magneto-optical disc in a state in which rotation of the magneto-optical disc is stopped. In a recording/reproducing operation, the magneto-optical disc starts to be rotated and the magnetic head slides on the surface of the magneto-optical disc and then floats. When the recording/reproducing operation is completed, the rotation of the magneto-optical disc is stopped again and the magnetic head slides on the surface of the magneto-optical disc to thereby come into contact therewith and stop. Such series of operations are called a CSS (Contact Start and Stop) system. In order to improve the durability due to the contact and sliding in this CSS system, the magnetic thin film of the magneto-optical disc is spin-coated with an ultraviolet ray setting type resin to thereby form a protective film.
In the recording-reproducing system using the magneto-optical disc as described above, however, the surface of the magnetic head and the surface of the protective film of the magneto-optical disc contact each other during the CSS and therefore, there has been the technical problem that the magnetic head is often stuck to the magneto-optical disc, whereby good access and good recording, reproduction and erasing of information are hampered.